little quiz

quiz.rs

#![feature(const_trait_impl)]

fn extend_lifetime(x: &str) -> &'static str {
    f::<S>(x)
}

const fn f<'a, T: Tr<'a> + ~const Drop>(x: &'a str) -> T::Ty {
    // can call g with T: Drop bound, even though
    // T: ~const Drop works for non-Drop-implementing types
    g::<T>(x)
}

#[allow(drop_bounds)]
const fn g<T: Drop>(x: &str) -> <T as Tr<'_>>::Ty {
    x
}

struct S;
trait Tr<'a> {
    type Ty;
}

#[allow(drop_bounds)]
impl<'a, T: Drop> Tr<'a> for T {
    type Ty = &'a str;
}

impl<'a> Tr<'a> for S {
    type Ty = &'static str;
}

fn main() {
    let x = "Hello World".to_owned();
    let s = extend_lifetime(&x);
    drop(x);
    println!("{s}");
}